Orb Sounds

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Orb Sounds Proposal from Mark Alexander 3-21-2007


The sound of chimes is simple, distinct and etheral. It doesn’t take a lot of energy to ring a chime loudly, making it possible to transmit sound over some distance on the playa without a large speaker or amplifier.

Electrically actuated chime

This consists of a single chime, mounted in a suspension, that is hammered by an electric solenoid. The chime could be a bar shape, bell shape or other shape (singing bowl, tube). High-efficiency bar chimes produce pure tones and are available in regular pitch intervals. Crotales could be used for a richer sound, though probably at the cost of efficiency (not as loud for the same striking force). Singing bowls would be richer still (but bigger and heavier as well).

Mounting one chime in each orb gives each orb a unique "voice." These chimes could be actuated in a number of interesting ways. They could be actuated in a coordinated fashion, or brownian-style at random intervals (decided by a random number generator in the orb).

In coordination (receiving signals from the mothership), chimes could be played in behaviors like call-and-response patterns. Or, different orbs coming into close proximity would "greet" each other. The mothership could also signal them to play in pre-scripted "pieces," perhaps in accompaniment to a pre-scripted dance.

Crotale sound sample: http://eamusic.dartmouth.edu/~travis/crotales/

Crotale wikipedia: http://en.wikipedia.org/wiki/Crotales

J.W.Stannard bar chime sound sample: http://www.equinoxbooksandgifts.com/assets/multimedia/invigoration.mp3

4-29-2007: Ordered a handful of solenoids for chime beater experimentation. Need to complete the solenoid driver circuit; this will require a FET power stage and a one-shot pulse output with variable pulse width. Expect to build this with AVR.

4-30-2007: Ordered one F6 crotale for experimentation

5-7-2007: F6 crotale is backordered until the end of May... guess I'll wait. SwarmSoundNotes 3.jpg

Passive chime(s)

A chime or set of chimes could be suspended in the orb in some kind of "card-in-the-spokes" fashion, making a random jingling when the orb rolls or changes direction


An amplifier and speaker mounted in each orb give the ability to play live re-enforced sound (motor whine) or pre-recorded sounds (music, soundbites, etc). In such a system the amplifier and speaker both need to be cheap, light, efficient, and probably small.

One example of a small high-efficiency amplifier is the Sonic Impact T-Amp. It runs on 12V, outputs 15W, costs $30, and consists of a 1"x3" PCB. This may or may not be enough power, as the playa tends to suck up sound.

Speaker horns are a high efficiency option, though they are usually directional. If non-directional sound were desired, multiple horns pointing in multiple directions could be used, a single horn could be pointed at the ground to disperse the sound, or it might be possible to find/produce a circular-output horn. Perhaps it's OK if the sound is directional, addressed out the "front" of the orb.

Multiple audio inputs could be selected from the amplifier, controlled by a manual switch or the mothership.

Sonic Impact T-Amp: http://www.tnt-audio.com/ampli/t-amp_e.html

4-10-2007: <Alexander> Started receiving shipments of various used car speakers; some 3.5" Blaupunkts and some 4" Subaru stock speakers. Without enclosures these are very weak in the midrange. Need to experiment with mounting these into enclosures to see how the sound changes. Also note that as small as it is, a 3.5" driver is pretty large when compared to the space available inside the orb, and this is without any enclosure.

4-15-2007: <Alexander> Ruled out the Sonic Impact T-Amp because it has two channels and they are not bridgeable (original plan was to bridge the left and right channels into one high-power channel).

4-29-2007: <Alexander> Mailordered a simple 7Watt mono amp circuit, $10. Try driving the Blaupunkt and Subaru speakers with it on arrival.

5-7-2007: <Alexander> Assembled 7Watt mono amp. It sounds pretty good, but doesn't have as much sound as the T-Amp.

5-9-2007: <Alexander> Tested the Blaupunkt 3"[1], Subaru 4", Altec 2.5" and Alltronix 0.75" [2] speakers with Sonic Impact T-Amp. Blaupunkt, Subaru and Altec were pressed against a cardboard box with a hole cut in it to isolate speaker front from back, increasing the loundess of middle and low frequencies. Altec has very low power handling, so it's out of the running. Subaru handles less power than Blaupunkt, and it's significantly larger (frame is about 4.5-5"), so it's out. That leaves the Alltronix 0.75" and Blaupunkt 3". Of these, it takes four of the Alltronix speakers running in parallel to come close to the sound output that the Blaupunkt has. Pros/Cons: Alltronix requires no additional enclosure, is fairly cheap (~$1.50) and with four drivers (~$6) the sound output should be more omnidirectional. Alltronix is not as loud as Blaupunkt (~$10), and mounting four of them is more complicated and may take up more space than one Blaupunkt with its inclosure. This Saturday 5-12-2007 I will put the Blaupunkt and Alltronix through their paces; measure sound pressure level and spectral content at 12 inches distance, and try to build them into more self-contained modules for trial in the orb (hopefully for integration on Sunday 5-13-2007). I'll also try to put mass and cost numbers to both. My gut feel is that even the 15W the Sonic Impact is giving us won't be enough, and when we go to an amp in the 30W-50W range, the Alltronix won't be able to keep up, and the Blaupunkt will look like the better option.

5-14-2007: <Alexander> Finished characterizing the speakers! My friend Joel and I, armed with a Phonic PAA2 Sound Analyzer, tried a handful of enclosures, everything from the speaker driver in free air, to mounting in a flat piece of 8"x10" cardboard, three lengths of 3" ABS tubing, and a 1 quart paint mixing tub. Since the 4" Subaru driver is big and has a paper cone (not durable, not waterproof), I didn't bother testing it, favoring the Blaupunkt, the Altec (it actually sounds pretty good in the enclosures!), and the little Alltronix speaker module. Results are in this spreadsheet Media: Altec&Blaupunkt_r2.xls‎ along with a writeup on the characterization procedures. Conclusion: The Blaupunkt has better power handling and deeper bass extension than the Altec. The "bucket" speaker cabinet seems to be the best enclosure, as it provides good midrange and bass response while keeping a relatively flat frequency profile. The tubes have better bass response, but at the cost of being very peaky - they have boosted response at some frequencies, and at other close frequencies, significant attenuation (big differences at close frequency spacing sound objectionable). A 15dB difference was measured between resonant peak and valley.

Sound Module Housing

The Sound Module Housing is both an enclosure for the Sound Module guts and a speakerbox. The eventual "beveled ABS Pipe" design is a sealed speakerbox design that contains the amplifier, MP3 player, memory and control MCU board. SwarmNotes 6-1.jpg

Motor Whine

A microphone or contact pickup on the servo(s) could be used as an input to the amplifier (through a simple preamp stage). This makes a rich an interesting sound coordinated with the movement of the orb. Note: Steering motor will probably be more interesting to listen to than the drive motor.

4-05-2007: <Alexander> Built one experimental preamp circuit with limited success; condenser mic seems not to be sentive enough and the circuit picks up a lot of EMI noise. Try improving the preamp circuit, and try moving to a contact pickup.

4-29-2007: <Alexander> Mailordered a $10 mic preamp circuit; see how its performance compares to the opamp circuit. Need to investigate pickup options - anyone has any piezo pickups lying around or experience in mounting them, contact Mark Alexander.

5-10-2007: <Alexander> $10 mic preamp doesn't have the necessary gain. Designing an op-amp based circuit around the OPA604, 2134, or AD712, as these have have high-impedance FET inputs, necessary for the low-current output of the piezo transducer.

Pre-Recorded Sound

An MP3 or other music storage + DAC device could be included as an input to the amplifier. This allows the ability to play music, separate voices of a coordinated piece of music, or individual soundbites. Sound files could be stored locally in each orb, and actuated by signal from the mothership. Using USB thumb drives are a good option for memory - once we figure out the directory structure, anyone could produce sounds to be played in the orbs, and changing out sound sets is as simple as changing out the USB drive.

Great source of samples at the Freesound archive: http://freesound.iua.upf.edu I fund this nightingale song inspiring...http://freesound.iua.upf.edu/samplesViewSingle.php?id=17185 <--- way cool!

4-5-2007: <Foote> Here's a cool mp3 player with a usb port for storage and serial control. You put mp3 files on a thumb drive, plug it in, then send it serial commands like "DIR FOO.MP3" and "VPF FOO.MP3" to test for and play back file FOO.MP3. http://apple.clickandbuild.com/cnb/shop/ftdichip?op=catalogue-products-null&prodCategoryID=55&title=VMUSIC Mark Alexander ordered one from Mouser and will test when it arrives. At $40 this is an expensive option.

4-28-2007: <Burnright> Here's a site with a bunch of MP3 player projects using AVR chips: http://www.myplace.nu/mp3/


Individual sound themes could be assigned to different days, different times of day, or different performances.

A simple sound theme would be to use motor whine during the day, and electrically actuated chimes at night.